1. Field of the Invention
The present invention relates generally to an inter-propellant seal in a turbopump, and more specifically to a hydrocarbon sensor in the inter-propellant seal.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a rocket engine turbopump, an inter-propellant seal (IPS) is necessary to separate the fuel from the oxidizer. If the two should mix inside the turbopump, they may likely ignite and cause a catastrophic engine failure. Depending on the engine cycle and turbopump configuration, the IPS may be required to separate the fuel rich turbine from the oxidizer pump, such as on the SSME (space shuttle main engine). For a single shaft turbopump, the IPS separates the fuel and the oxidizer pumps.
A typical IPS used in a turbopump is shown in FIG. 1. There are generally at least three discrete seal components. An inert gas, such as helium or nitrogen, is used to provide a buffer or barrier zone between the two propellants. In addition to the seals themselves, the two sources, the two drains and the buffer gas supply require equal attention in design. During operation, the buffer cavity pressure is always maintained higher than either of the adjacent drain pressures in order that the two volatile fluids do not mix. However, in the event that the fluids do mix, the turbopump should be shut down immediately. Currently, the prior art does not have any process involved to determine if the fuel is mixing with the oxidizer in the inter-propellant seal.
A re-usable engine whose fuel is rocket propellant (RP), a higher grade version of kerosene, presents a unique ground support requirement. After the engine has been run once, what is typically done is to maintain the buffer purge flow continuously for 24 hours 7 days per week. This is done because all of the leftover kerosene residue cannot be removed from the pump, and over time this residue may wick between the seals over the oxidizer drain cavity and even to the oxidizer side of the pump. Wicking is when the fluid slowly flows along the surface while sticking to the surface. If one chooses not to continuously run the buffer purge flow, one runs the risk of kerosene wicking to the oxidizer side of the pump and causing a catastrophic failure upon the next use of the engine.
What is currently done is to run the buffer purge flow continuously in-between uses of the engine. If the ground support requirement of continuous buffer purge flow cannot be met, another option is to place some type of a hydrocarbon detection sensor in the oxidizer drain cavity. During the pre-flight checklist, when the purge flow is started the hydrocarbon sensor would detect whether or not kerosene has wicked over to the oxidizer drain cavity. If this has happened, it would require an engine tear-down to clean all the areas of the turbopump where the oxidizer flows.